Process of heating steel for hardening



Patented Mar. 3, 1936 UNITED STATES PATENT OFFICE Frederick Jarvis, Philadelphia, Pa.

No Drawing. Application April 2, 1934, Serial No. 718,682

1 Claim.

My invention relates to a novel and useful process for the heating of metals, and more particularly for the heating of steel in such operations in which hardening is a desirable and re- 5 quired characteristic. It has been previously the practice to pass the steel tools, implements and stock to be hardened into a bath of molten lead having a temperature of 1400 F. to 1550 F. and subsequently to immerse the steel parts in a quenching solution in order to obtain the quality of required hardness. Such a process is productive of uncertain results in that the lead of the lead bath frequently adheres to scattered areas of the steel stock and induces the development of soft spots in the steel stock when it is hardened in the quenching solution.

A primary purpose of my present invention is to cover the bath of molten lead with a supernatant layer of fused chlorides in order that the 20 steel stock that is immersed in the molten lead may be withdrawn after sufficient heating entirely free and clean of lead before it is plunged into a saline solution in which the hardening proceeds uniformly to the achievement of a homogeneously hardened and brightly burnished steel stock.

In my improved process I have also observed that the layer of chlorides imposed upon the molten lead eliminates the drossing of the lead, an undesirable condition that impairs the subsequent uniform hardening of the steel stock. Accordingly, in my process in which dross is eliminated, the steel stock when removed from the lead bath passes through the layer of fused 35 chlorides and not through the superficial dross that collects at the surface of the lead in any of the conventional processes.

In carrying out my invention, I prefer to use a mixture of compounds in dry and powdered 40 form which is added to the molten lead at a temperature of 1400 F. to 1550 F. To accomplish the results of clean and uniform hardening, I have discovered .and perfected a formula for this mixture which is sufficiently precise to enable anyone skilled in the art to secure a homogeneous hardening of steel parts, tools, devices, etc. of .5% to 1.5% carbon content. Before disclosing my novel formula, I wish to declare that it is intended to be illustrative of my invention and not limiting, and that any substantial equivalents of the ingredients hereinafter described may be used without departing from the scope of the spirit of my invention or sacrificing any of its advantages.

Upon the surface of the molten lead of the lead bath I pour a mixture in solid and powdered state of barium chloride, potassium chloride and sodium chloride in substantially the proportions of 45%, 45% and respectively. The mixed chlorides fuse into a supernatant liquid of approximately or more in thickness. Since the temperature of the lead bath is approximately 1500 F. the formation of the layer of molten chlorides is rapidll obtained. The steel stock to be hardened is first warmed slightly by any extraneous method but only for the purpose of removing the chill in case the temperature of the stock is somewhat below a normal temperature (100 F. or more). The stock is then plunged through the layer of fused chlorides and completely immersed in the molten lead. This initial passage through the chlorides superficially coats the entire area of the stock and prevents the lead from adhering to its surface anywhere while the stock is being heated to the desirable temperature. When the stock is withdrawn from the molten lead it again passes through the supernatant layer of the chlorides and as it leaves the bath it is strikingly free of the minutest traces of lead.

The stock then in a condition of high temperature, devoid of lead and thinly coated with the mixed chlorides is plunged into an aqueous solution of sodium chloride of a specific gravity of approximately 1.045. As soon as the hot stock strikes the cold saline solution the superficial coating of the chlorides is cracked away and the quenching action of the cold bath hardens the steel into a glistening and uniformly hardened object entirely devoid of soft areas and excellently adapted to the manufacture of tools like files, taps, dies, etc.

I appreciate that various modifications may be made in the formula of the ingredients and in the steps of the process without departing from the spirit of my invention, and reserve the right to all such deviations that are fairly embraced within the scope of the following claim.

I claim: l

A process of heat treating steel for hardening which consists in superimposing upon a lead bath at a temperature of substantially 1400 F. to 1550 F. a superficial layer of solid salts, which consist of substantially 45% barium chloride, 45% potassium chloride, 10% sodium chloride and readily fuse into a supernatant liquid, then passing the steel to be treated downwardly through said fused salt layer into said lead bath, then upwardly through said lead bath and said fused salt layer and then quenching the steel in an aqueous solution of sodium chloride of an approximate specific gravity of 1.045.

FREDERICK JARVIS. 

